Hi All,
My Dad and I have tried many things to resolve our overheating Bukh but not having much luck.

The overheating has slowly increased over time to the point now where after only 5mins of running, the engine will get up to 100deg, prompting the alarm to go off. With the use of a temperature gun we've ascertained the back part of the block near the thermostat is noticeably hotter than the rest of the engine.

Things we've done:
- Checked impeller & volume of water exiting the engine
- Flushed / soaked cooling system with vinegar solution, Rydlyme and then moved to a hydrochloric acid mix
- Removed and cleaned the Y and adjoining hoses
- Replaced the exhaust elbow as we found a crack
- Removed and cleaned the exhaust manifold
- Bypassed the hot water system in case that was somehow the culprit

From what we gather next step may be taking off the head to check if there's a blockage we haven't managed to remove. This may be a bit beyond us.

Any advice at this point would be much appreciated.

Cheers,
Ed

With the use of a temperature gun we've ascertained the back part of the block near the thermostat is noticeably hotter than the rest of the engine.

Here is a post on the British "Yachting and Boating Weekly" site which points to a thermostat seizure problem.
At least a thermostat removal will allow you to peek into the block and see how successful your anti scaling (vinegar etc) was.
forums.ybw.com/index.php?threads/bukh-dv20-thermostat.195658/
gary

Yep, take out the thermostat, put it in a pot of water and put pot on stove, see if it opens around 60-65degree if raw water cooled if opens at higher temp(80-90) thermostat maybe from fresh water cooled motor. Prior check that it's not all gunked up. Replace if not opening smoothly. If buying a new one, specify Raw water or Fresh Water cooled... they are different temps opening.

Secondly, after the Y piece, where it enters the engine block, did you take out the steam probe or what ever it's called? There should be 2 bolts, hard to get to, but the probe is basically a metal tube about 10mm, and 100mm long with a blocked end and small hoses drilled in it, they can block easily, then all water will bypass Y and go over the top of thermostat.

After you checked Steam probe and Thermostat, search my post on overheating Bukh 24, I had micro air bubbles leaking in from hose from seacock hose, couldn't see until I changed to clear hose, once tightened, overheating stopped..

www.seabreeze.com.au/forums/Sailing/General/Bukh-Overheating-and-the-unexpected-solve.

I would start at Theromstat, it's easy access, easy to test, you can scrap/clean the inside of housing, and will likely fix your issue, just take out a second mortgage and ring the boys at Taren Point and buy one..

www.cruisersforum.com/forums/f54/marine-diesel-thermostats-not-what-they-seem-122461.html

Thermostat works differently to probably how your thinking.... interesting read

www.cruisersforum.com/forums/f54/marine-diesel-thermostats-not-what-they-seem-122461.html

lmowners.proboards.com/thread/290/bukh-water-temperature-indication-cycling?page=2
Also picture of Steam poker down page, after Y piece.

i still think the thermostat!!

Sounds like the thermostat and or the bypass set up. Do not pull off the head. I have not checked but the heads on some marine diesels like my Volvo do not have water cooling passages. The raw water just circulates through the manifold and block. If you do remove the thermostat and run the engine with out it ensure the water will circulate.

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Ramona said..
Sounds like the thermostat and or the bypass set up. Do not pull off the head. I have not checked but the heads on some marine diesels like my Volvo do not have water cooling passages. The raw water just circulates through the manifold and block. If you do remove the thermostat and run the engine with out it ensure the water will circulate.

If you remove thermostat, then you have to block off the Y where it goes to top of thermostat, otherwise water will take the path of least resistance and not circulate through the block well.

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Cabron said..
Yep, take out the thermostat, put it in a pot of water and put pot on stove, see if it opens around 60-65degree if raw water cooled if opens at higher temp(80-90) thermostat maybe from fresh water cooled motor. Prior check that it's not all gunked up. Replace if not opening smoothly. If buying a new one, specify Raw water or Fresh Water cooled... they are different temps opening.

Secondly, after the Y piece, where it enters the engine block, did you take out the steam probe or what ever it's called? There should be 2 bolts, hard to get to, but the probe is basically a metal tube about 10mm, and 100mm long with a blocked end and small hoses drilled in it, they can block easily, then all water will bypass Y and go over the top of thermostat.

After you checked Steam probe and Thermostat, search my post on overheating Bukh 24, I had micro air bubbles leaking in from hose from seacock hose, couldn't see until I changed to clear hose, once tightened, overheating stopped..

www.seabreeze.com.au/forums/Sailing/General/Bukh-Overheating-and-the-unexpected-solve.

I would start at Theromstat, it's easy access, easy to test, you can scrap/clean the inside of housing, and will likely fix your issue, just take out a second mortgage and ring the boys at Taren Point and buy one..

www.cruisersforum.com/forums/f54/marine-diesel-thermostats-not-what-they-seem-122461.html

Thermostat works differently to probably how your thinking.... interesting read

www.cruisersforum.com/forums/f54/marine-diesel-thermostats-not-what-they-seem-122461.html

Thanks Cabron,

We were actually running it without a thermostat for a while not realising that can cause overheating - you're right it operates differently to what we were thinking. However we have since put in a new one which we picked from Bukh at Taren Point, also taken it out and tested on the stove - still overheating.

I believe we did take out the steam probe when we took off the Y, as it's attached to the Y? there was a bit of gunk built up which we took care of before reassembling.

We have replaced the hose(s) from the seacock going into the pump and checked clamps are good after reading up on your air bubble issue, however maybe worth doing again with clear hose as a way of ruling that out. We had also put a filter in place but have since removed while we trouble shoot the overheating issue.

Back to the drawing board for now....

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garymalmgren said..
With the use of a temperature gun we've ascertained the back part of the block near the thermostat is noticeably hotter than the rest of the engine.

Here is a post on the British "Yachting and Boating Weekly" site which points to a thermostat seizure problem.
At least a thermostat removal will allow you to peek into the block and see how successful your anti scaling (vinegar etc) was.
forums.ybw.com/index.php?threads/bukh-dv20-thermostat.195658/
gary

Thanks Gary,

We have replaced thermostat but unfortunately hasn't done the trick

I would suggest rigging up a 12v pump and pump phosphoric acid through the system starting at the hose off the saltwater pump. Use a plastic drum in the system to recirculate the acid. Watch a few "Barnacle Buster" youtube clips and see how they do it.

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Ramona said..
I would suggest rigging up a 12v pump and pump phosphoric acid through the system starting at the hose off the saltwater pump. Use a plastic drum in the system to recirculate the acid. Watch a few "Barnacle Buster" youtube clips and see how they do it.

Google around, there's a diagram, means remove impeller if connected to seacock side, and clamp the Y bypass so the acid goes through the block, as well as remove the thermostat, catch water after the exhaust elbow.
Is your temp sensor 1 or 2 pin? One is resistance, 2 pin has a switch and resistance. Some DV20's have a issue with sender. Something to do with clearance in housing, this forum has a thread on it.
Have you taken out the anode? Is there gunk inside? There's also a plug on side of block, which you could pump out from, plug is on side, behind start motor, other end of block.

So, unless water is blocked, so acid flush, Y is clear, thermostat OK, exhaust elbow clear, there's not much else. The bubbles I spoke about were very small, only saw when shaking the hose when could see a couple... seriously never thought a issue, hence took a while to find.
The beauty with a Bukh is, it is very simple.
My thermostat housing also had a build up, so much so, when I took the plug out from next to sender, no water came out, scrapped with screwdriver to clear.

Also some have drillled bigger holes in steam probe, get more water flowing in block.

If acid flushing, also leave sit for awhile before pumping, some leave it hours to breakdown the deposits, always filter the output so you don't pump deposits back into block which will settle.

Unlikely, however put temp sender in pot and heat up to make sure it's not going off under temp??? Should be around 90-96 degrees??

Aslo google different acids, some use CLR, or brick cleaner... I'm yet to have to do, so can't advise

1st picture- No. 17 plug on block to drain, could be used to pump in/out from with acid

2nd picture- No. 13, steam probe, DV20 had really small holes in it, can be drilled out a little, most common to block.

CLR works but is very slow. I did trials some time back comparing CLR, vinegar and Metal Gleam. Metal gleam is a mixture of acids but mostly phosphoric, I'm sure it's similar to Barnacle Buster but at 1/10 the price. I used glass jars with a few seashells in them and used the same amount in each jar. The CLR I used about 2:1, Metal Gleam 5:1 and straight vinegar. All worked but the vinegar and CLR were painfully slow. The Metal gleam dissolved the calcium seashells in a couple of minutes. I also put the mixture in a cast-iron engine manifold with other metals used in engines and left it overnight to see what effect it had. The metals were just very clean. I should add that the acid will etch aluminium. The first time I cleaned my engine coolant passages I just filled it with the Metal Gleam mixture and went off fishing for a couple of hours!

Anyone tried this yet ?
www.supercheapauto.com.au/p/evaporust-evapo-rust-rust-remover---5-litre/354058.html

They also make a product to clean engine blocks but harder to find in Oz,

evapo-rust.com/thermocure/

Metal Gleam is under $40 for 5 litres.

Harb, I haven't tried the evaporust but the other product in the link rust remover gel ain't worth a pinch of Sh.., It sorta works then you have a gooey rusty blackish mess to deal with, horrible.
Ramona, the metal gleam looks like a good thing and and cheaper than the Bunnings rust buster by a long shot. But hang on I just found kegland brew supplies selling 96% phosphoric acid $6.45/ 500ml.
I think I can smell a rat, could the big green shed and our big auto outlets be taking advantage of us ?

Yeah but is also a CLASS 8 chemical.

Haven't used Metal Gleam itself but from the SDS it looks like a phosphoric acid based converter/remover , same as the Ranex I use now. And I do know that Ranex burns the skin , stinks when reacting with rust and it puts holes in the concrete floor when spilled. It also stings when paint brush bristles spring back and send a fine mist of acid into the face and behind the glasses. After the last time I won't be using it again without a full facemask and long sleeves for me and plastic sheets for the garage floor.

The reason I asked about the Evaporust is that I've seen it used on Youtube videos to clean up stuff and seems to work well at removing the rust without affecting good metal or surounding paint , is not corrosive, non toxic and can get it all over the hands. Apparently it is also reusable so for smaller parts I could drop them into the solution then pour it back in the bottle to reuse next time instead of having to discard it like I do with Ranex.

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Harb said..
Yeah but is also a CLASS 8 chemical.

Haven't used Metal Gleam itself but from the SDS it looks like a phosphoric acid based converter/remover , same as the Ranex I use now. And I do know that Ranex burns the skin , stinks when reacting with rust and it puts holes in the concrete floor when spilled. It also stings when paint brush bristles spring back and send a fine mist of acid into the face and behind the glasses. After the last time I won't be using it again without a full facemask and long sleeves for me and plastic sheets for the garage floor.

The reason I asked about the Evaporust is that I've seen it used on Youtube videos to clean up stuff and seems to work well at removing the rust without affecting good metal or surounding paint , is not corrosive, non toxic and can get it all over the hands. Apparently it is also reusable so for smaller parts I could drop them into the solution then pour it back in the bottle to reuse next time instead of having to discard it like I do with Ranex.

It's not rust that's trying to be removed, it's a calcium deposit left from saltwater cooled motors. There generally isn't much rust as such inside the block, I guess the anode takes care of that, so yes a acid is required, as mentioned vinegar does the job, just takes time. And once the acid is neutralised it stops working, hence multiple repeats are necessary. A stronger acid breaks it down quicker, however like any acid, great care must be taken.
Like when cleaning a saltwater head, you can use bleach and scrub forever, and barely does anything, but a couple good pours of vinegar, and it's super clean.. just a chemical reaction

I have used Evaporust on old rusty tools. Does the job well, no rust left, just pitting for the really bad spots and good metal on the surface rust. Although there is no real surface rust...there is always some form of loss, by definition as the surface has reacted to form the rust. What it does best is clean the really deep rust that you can't dig out other than chipping which only makes it worse.

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woko said..

Ramona, the metal gleam looks like a good thing and and cheaper than the Bunnings rust buster by a long shot. But hang on I just found kegland brew supplies selling 96% phosphoric acid $6.45/ 500ml.
I think I can smell a rat, could the big green shed and our big auto outlets be taking advantage of us ?

Metal Gleam is made by Nowra Chemicals. They make a lot of stuff for other big-name labels as well. My son used to be a chemist there and would not reveal the other brand names.

@ MEGAMAX Thanks, I'm ok with pitting left from removing the rust as 2-3 coats of primer would cover that. As long as all the rust is cleaned up properly, with Ranex I found that is not always the case as I had rust return 1-2 years later.

@ woko Don't know about the gel. I've seen a youtube clip of some guy restoring an old pushbike using paper towels with evaporust wrapped around a bike part too long to fit in the container then using glad wrap to make sure it didn't dry overnight. Was impressed by the results as the rust disappeared instead of just being converted like with phosphoric acid.

@Cabron With the outboard I've been using Salt Off once a year to flush off the salt minerals. I see Whitties has something called Desalt which is also used for flushing the salt minerals but also removes light corrosion. Biodegradable and non- toxic so probably some fancy vinegar formula.